Organo-substituted polyphosphazenes are usually made by reacting a solution of a polyphosphonitrilic chloride with a solution or slurry of an alkali metal (e.g. sodium) alkoxide, aryloxide or mixtures thereof including substituted alkoxides and aryloxides. This forms an alkali metal salt (e.g. NaCl) in extremely finely divided form. Attempts have been made without much success to remove this salt by filtration. Better results have been achieved by washing the reaction solution with water to dissolve the salt into the aqueous phase and then removing the aqueous phase. However, phase separation even after acid neutralization is a constant problem and in some cases the resulting emulsions will not separate at all. Accordingly, a need exists for a polyphosphonitrilic halide substitution process which permits removal of most of the by-product salt without formation of a stable emulsion.